THE ETHMOID BONE. 2J 



Muscles of Mastication, 3 the temporal, external and internal pterygoids. 

 Superior constrictor, tensor palati, and laxator tympani, 3. 



THE ETHMOID BONE. 



Describe its General Characteristics. It is a spongy, light bone, de- 

 pending from the ethmoidal notch of the frontal, and from between its orbital 

 plates. It consists of a body and 2 lateral masses, and is named from the Greek 

 word j)0//of, aytkmos, a sieve. 



What are the Points on its Body ? The body** consists of a horizontal 

 or cribriform plate, and a perpendicular plate, and presents the 

 Crista Gallif or cock's comb, projecting up- 

 wards, for the attachment of the anterior end 

 of the falx cerebri. 



Cribriform Plate,d on each side of the crista 

 galli. It is concave for the olfactory 

 bulbs/ and perforated for the transmission 

 of the olfactory nerves, the nasal branch 

 of the ophthalmic nerve, and numerous 

 small vessels. 



Perpendicular Plate^ assists to form the nasal 

 septum, is usually inclined to one side, 

 grooved for filaments of the olfactory 

 nerves, and has attached to it the cartilage of the nose. 

 Describe the Lateral Masses. They consist of a number of cellular 

 cavities, and each one presents the following points, viz. 



Ethmoid Cells, the anterior opening by the infundibulum into the middle 



meatus of the nose, the posterior into the superior meatus. 

 Os Planum,h or orbital plate, helps to form the inner wall of the orbit, and is 

 notched superiorly to form with the frontal bone the two ethmoidal foramina. 

 Unciform Process, descends to articulate with the inferior turbinated, and 



forms part of the inner wall of the antrum. 



Superior Turbinated Process, f curves downwards and outwards. 

 Middle Turbinated Process, g is larger and more curved than the superior. 

 These processes bound the superior meatus of the nose, and are often 

 called the superior and middle turbinated bones. 



Describe its articulations, development, and muscles. The ethmoid 

 articulates with 15 bones, viz. all those of the face except the malar, and the 

 frontal and sphenoid of the cranium. It is developed by 3 centres, I for each 

 lateral mass, and I for the body, ossification being completed about the 6tb 

 year. There are no muscles attached to it. 



